[GHC] #5316: Orphan instances strike again: ghc rejects a program at first but will accept it if you repeat the same compilation command

[GHC]

#5316: Orphan instances strike again: ghc rejects a program at first but will
accept it if you repeat the same compilation command
-------------------------------------+-------------------------------------
        Reporter:  jcpetruzza        |                   Owner:
            Type:  bug               |                  Status:  closed
        Priority:  low               |               Milestone:  ⊥
       Component:  Compiler          |                 Version:  7.0.4
      Resolution:  duplicate         |                Keywords:
Operating System:  Unknown/Multiple  |            Architecture:
 Type of failure:  GHC rejects       |  Unknown/Multiple
  valid program                      |               Test Case:
      Blocked By:  2182              |                Blocking:
 Related Tickets:                    |  Differential Revisions:
-------------------------------------+-------------------------------------
Changes (by ezyang):

 * status:  new => closed
 * resolution:   => duplicate
 * blockedby:   => 2182


Comment:

 I was reviewing orphan instance tickets, and I think this one was fixed by
 #2182; Simon's analysis is essentially the same.  I can't actually test it
 on the test-case given because `System.Event.Manager` has changed since
 then.

 The one thing that you might find puzzling is the situation with
 optimization: but actually it is simple to explain: optimization simply
 means we might tug on more `ModIface`s because we have to process
 unfoldings, etc. With the fix for #2182, the orphan instances that are
 pulled in from this process are unaffected.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/5316#comment:5>
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